Table of Content

24 September 2012, Volume 30 Issue 5

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Communication Engineering

Effect of Imperfect Frame Synchronization on Linear Interpolation of Amplititude and Phase

SONG Lei1, LI Li-hua1, GAO Xiang-chuan2, PEI Yu-shan1, WANG Hua-lei1

2012, 30(5):  441-447.  doi:10.3969/j.issn.0255-8297.2012.05.001

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In orthogonal frequency division multiplexing (OFDM) systems, a common interpolation method is the linear interpolation in in-phase and quadrature components (I-Q interpolation). Linear interpolation of amplitude and phase (A-P interpolation) is rarely used in practice since it is inferior to I-Q interpolation in terms of performance and computational complexity. For imperfect frame synchronization,  the effect of cyclic prefix (CP) removal prior to the A-P interpolation is studied and compared with I-Q interpolation. A universal expression of mean square error in A-P and I-Q interpolations is given. Analyses show that A-P interpolation mainly depends on frequency correlation of the channels, and is less affected by preact of CP removal, while
I-Q interpolation is affected by both frequency correlation of the channels and preact of CP removal. Thus, A-P interpolation can also be used when the synchronization performance is poor.

Modified Bidirectional Decision-Feedback Equalizer for Two-Ray Fading HF Channels

SHAO Han-qin, XU Da-zhuan, WANG Lei

2012, 30(5):  448-454.  doi:10.3969/j.issn.0255-8297.2012.05.002

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In this paper, we consider the use of a bidirectional decision-feedback equalizer (BiDFE) in two-ray fading HF channels. A low-complexity modified BiDFE using the properties of these channels is proposed. Coefficients of the equalizer are optimized, and the outputs of forward DFE and time-reversal DFE are combined using maximal ratio combining (MRC) rules. Theoretical analysis and computer simulations show that the proposed scheme completely cancels inter-symbol interference (ISI) between the two streams so that signal-tonoise ratio (SNR) is the sum of SNRs of the two streams. The performance of modified BiDFE is superior to conventional DFE and bidirectional arbitrated DFE (BAD), while the computation complexity is lower than BAD.

Threshold-Based Feedback Scheme for Multi-beam Opportunistic Beamforming in OFDMA System

LIU Shan1, YANG Wei1;2

2012, 30(5):  455-460.  doi:10.3969/j.issn.0255-8297.2012.05.003

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 Multi-user MIMO-OFDMA is an important technology in the future wireless communications. In MIMO-OFDMA system, a large amount of feedback information has to be used to achieve multiuser diversity when all users are exploited. To deal with the problem, a multi-beam opportunistic beamforming scheme is proposed, in which partial multiuser diversity is achieved by setting a feedback threshold. Each user calculates the received signal to interference-plus-noise ratio (SINR) of each beam at individual subcarriers. The SINR value is transmitted to the base station only when it is larger than the threshold. The threshold is optimized to guarantee a target average resource utilization rate. The amount of feedback in the proposed scheme is quantified, and it is proved that feedback is limited to a fixed level. Simulation results indicate that optimal threshold can be determined effectively from a predefined resource utilization rate. Also, the feedback load can be reduced significantly with little capacity loss.

Parallel Decoding of Turbo Codes in Covert Communications

ZHAO Dan-feng, ZHU Tie-lin, XUE Rui

2012, 30(5):  461-465.  doi:10.3969/j.issn.0255-8297.2012.05.004

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In covert communication with low signal-to-noise ratio, Turbo codes are used as channel coding to improve system reliability. A parallel decoding algorithm is proposed by inserting tail bits to reduce decoding delay and improve confidentiality. The periodical tail bits make the encoder return to a known status. In the decoder, the initial values of sub-blocks can be obtained from the zero-tail bits. The random tail bits can be viewed as pseudo information. Thus, confidentiality of the communication is enhanced. Simulation results show that, compared with conventional parallel decoding methods, the proposed scheme can improve Turbo decoding rate and reduce time delay without performance loss due to unknown boundary. The algorithm is suitable for high-speed communications in a low SNR environment.

Interleaving Differential MMSE Multiuser Detection Based on Cyclic-stationary Period

FENG Xing-le, LI Wei, JIANG Yun-guo

2012, 30(5):  466-472.  doi:10.3969/j.issn.0255-8297.2012.05.005

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To suppress multiple access interference (MAI) in wide code division multiple access (WCDMA) systems in a fast fading channel, an interleaving differential MMSE multiuser detection method based on the cyclo-stationary period is proposed. According to typical characteristics of two-layered spreading modulation in WCDMA, the update criterion of coefficients is based on the cyclo-stationary period, instead of the spread factor. As the proposed method can characterize the pattern of MAI properly, improved performance can be achieved. Moreover, interleaving is involved to let the symbols with the same comprehensive spread sequence be transmitted consecutively to ensure that the channel gains of successive symbols keep constant in the fast fading channel. Simulation results show the performance is improved without increasing the system complexity, and Doppler shift is better dealt with.

Flow Control of Optimum Second Order Approximation Modulus with Improved Differentiation Element in Sensor Networks

NI Xiao, SHI Wei-ren, HUANG Qin

2012, 30(5):  473-478.  doi:10.3969/j.issn.0255-8297.2012.05.006

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Because self-organized wireless sensor network is randomly setup, data transmission among the nodes is subject to traffic jam. To address this problem, this paper proposes a method of optimum second order approximation modulus with an improved differentiation element to control data transmission. The controller applies a function of the optimum second order approximation modulus as its transfer function. It negatively
feedbacks the data buffer length in a node to its input point, and controls the speed of data transmission of the up-stream node. A differential element is added to the transfer function to reduce over-modulation and speed the peak emergence. Thus no traffic overflow will occur both in transition and in permanent periods.

Impact of Relay Location on SER for Amplify-and-Forward Cooperative Communications

LI Yun1;2, HUANG Qing1

2012, 30(5):  479-486.  doi:10.3969/j.issn.0255-8297.2012.05.007

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In this paper, we analyze the symbol error rate (SER) for end-to-end link in amplify-and-forward (AF) cooperative networks. An optimal relay position is made by setting the distance between nodes. A multihop relay selection algorithm based on channel state information (CSI) is proposed, which is the expansion of single-hop relay selection to ensure the lowest SER of the cooperative node. A multi-hop relay selection algorithm based on node position is then investigated according to the impact of node position on system performance. Simulation results indicate that the optimal multi-relay position is at the midpoint between the source and destination nodes, and the multi-hop method provides significant performance gain in terms of total energy over the exiting AF relay selection algorithms.

Distributed Resource Allocation in HeNB Networks

WANG Shuang-die1;2;3;4, WANG Jiang1;2;3, XU Jing1;2;3, TENG Yong5, HORNEMAN Kari

2012, 30(5):  487-492.  doi:10.3969/j.issn.0255-8297.2012.05.008

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A distributed algorithm is proposed for resource allocation in self-organized home eNodeB (HeNB)networks. In this algorithm, each HeNB selects component carriers (CC) based on the network status. If a reselection request is received from neighboring cells, the HeNB will reselect the CC in the backup CC list, and release the CC requested by neighbors to enhance possibility of successful carrier selection. Each HeNB then adaptively performs power optimization in active CCs to reduce inter-cell interference and enhance the system capacity. Simulation results show that this resource and power allocation algorithm can enhance average user throughput and reduce the outage rate.

Signal and Information Processing

SAR Image Resolution Selection for Ground Moving Target Indication

YU Jing1, YANG Zhi-wei2, LI Ya-an1

2012, 30(5):  493-497.  doi:10.3969/j.issn.0255-8297.2012.05.009

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In the technique of ground moving target indication using SAR (SAR-GMTI), the image resolution has great impact on the target detection performance. A SAR image resolution selection scheme is proposed in this paper. Performance of target detection at different image resolutions is analyzed in view of the detection probability. Based on the analysis and taking a target with classical RCS as an example, optimal SAR resolution for different target size is given. Simulation results indicate that the scheme can be widely used in engineering practice.

SAR Image Classification Based on SVM with Fusion of Gray Scale and Texture Features

FU Zhong-liang, ZHANG Wen-yuan, MENG Qing-xiang

2012, 30(5):  498-504.  doi:10.3969/j.issn.0255-8297.2012.05.010

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This paper proposes a set of SVM classification methods based on fusion of gray scale and texture features. A set of experiments are carried out using the SVM classifiers with feature fusion. Both qualitative and quantitative approaches are applied to assess the classification results. Experimental results demonstrate that the proposed approach is effective for SAR image classification with accuracy higher than those obtained by using single texture feature based algorithms.

Image Enhancement for Sonar Images Based on Surfacelet and Multi-scale Retinex

FU Qiang1, LI Yi-bing1, TANG Chun-rui2

2012, 30(5):  505-510.  doi:10.3969/j.issn.0255-8297.2012.05.011

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Due to complicated underwater channels and various interferences, sonar image resolution is low,leading to difficulties in identifying edge details. Many enhancement algorithms can improve image resolution without de-noising. To this end, the paper proposes an improved enhancement algorithm, which first performs de-noising using surfacelet transform with adaptive threshold, and then carries out multi-scale retinex enhancement.
Simulation results show that the proposed algorithm has advantages in preservation of edge details color information. It helps subsequent image processing.

Spatial Relation-Aided Method for Object-Oriented Extraction of Buildings from High Resolution Image

ZHOU Jun-qi, LI Zhi-juan

2012, 30(5):  511-516.  doi:10.3969/j.issn.0255-8297.2012.05.012

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Based on the characteristics of high spatial resolution images, an object-oriented approach to the building extraction is proposed. The method takes the object as a processing unit to perform classification using the rich information such as the spectrum, the object shape, and the implicit space semantic relations embedded in the images. The classification result is optimized based on the characteristics of the spatial relationship. Edges between different categories are modified using mean filtering. Experiments show that the object-oriented method can provide relatively complete extraction of the building, and improve precision of the extraction.

A New Adaptive Bilateral Filtering

YU Bo, GUO Lei, QIAN Xiao-liang, ZHAO Tian-yun

2012, 30(5):  517-523.  doi:10.3969/j.issn.0255-8297.2012.05.013

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In the existing bilateral filtering algorithm, the domain parameters and range parameters need to be predefined. Parameters of a bilateral filter are fixed and cannot guarantee to be optimal. A new adaptive bilateral filtering (ABF) is proposed in this paper. The ABF obtains the domain parameters by estimating the local object scale to minimize edge blurring. The range parameters are set adaptively according to noise variance estimated in smooth areas of a sub image. The method can improve the filtering performance. To filter out strong noise, the value of domain parameters is increased. ABF avoids setting parameters solely by experience, and the domain parameters are set adaptively according to the local image features. ABF can improve the noise filtering ability and reserves edges. Experiments show that the adaptive bilateral filter is superior to traditional bilateral filters, anisotropic diffusion filters, and modified bilateral filters in both subjective and objective evaluations.

A Novel Invisible and Private Flow Watermarking Scheme

ZHANG Lian-cheng, WANG Zhen-xing, XU Jing

2012, 30(5):  524-530.  doi:10.3969/j.issn.0255-8297.2012.05.014

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Existing active flow watermarking techniques introduce significant delays to target flows, enabling attackers to detect and remove the inserted watermark from the flow, and even duplicate them to unmarked flows. We propose a novel invisible and private flow watermarking scheme that embeds watermarks in randomly chosen inter-packet delay positions. Different pseudo-noise codes are used across multiple network flows
by slightly manipulating the arrival times of the packets. Theoretical analysis and experimental results demonstrate that the proposed scheme is robust against timing perturbation, effective in detecting multiple network flows, and invisible to timing analysis attack based on the Kolmogrov-Smirnov test.

Detection of Small Surface Defects Based on Machine Vision

HE Zhi-yong1;2, SUN Li-ning1;2, RUI Yan-nian1

2012, 30(5):  531-537.  doi:10.3969/j.issn.0255-8297.2012.05.015

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This paper proposes an effective method to be used in fast detection of small surface defects. The space domain gradient method is useful to enhance the surface image. However, we show that the Otsu method cannot produce satisfied result in segmenting small defects in a large surface image. To detect small defects and improve the performance of Otsu method, an algorithm based on the distribution of variances of image blocks is developed to search of small defect regions. Analysis and experiments show that the proposed method can be applied for fast detection of small surface defects.

Rectal Perception Function Rebuilding Based on Wavelet Packet Analysis and Support Vector Machine

JIANG En-Yu, Zan-Feng, Shu-Xiao-Jin, Shao-Yong, Wang-Xiao-Hua

2012, 30(5):  538-544.  doi:10.3969/j.issn.0255-8297.2012.05.016

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To solve the problem of rectal perception loss caused by anal incontinence, a rectal perception function rebuilding method is proposed based on wavelet packet analysis and support vector machine (SVM). By analyzing the characteristics of human rectum, high-amplitude propagated contractions (HAPC) in rectal contractions are used to indicate an urge to defecate. Feature extraction of rectal pressure is done using wavelet packet analysis, and take L2 norm and standard deviation of decomposition nodes as eigenvector. A rectal perception prediction model is trained using SVM. By extracting eigenvector from rectal pressure signal, penalty factors and slack variables are cross validated and optimized. Then the trained model is used to predict the urge to defecate. Prediction accuracy of the feed-forward neural network and SVM with different kernel functions is compared. Experiment results show that the proposed method is effective to rebuild patients’ rectal perception function.

Control and System

Real-Time Assisted Decision-Making in Air Fighter’s Penetration Attack

CHEN Zhong-qi, YU Lei, SUI Yong-hua, ZHOU Zhong-liang

2012, 30(5):  545-551.  doi:10.3969/j.issn.0255-8297.2012.05.017

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Assistant decision-making is important in air fighter’s penetration attack, especially for pilots to lighten flying burden and reduce operation mistakes. The air fighter kinematic and dynamical models, and the threat constraint and fire control border constraint models are built. Based on these models, an assistant decision-making model for air fighter’s penetration attack is established. Using the Legendre pseudospectral method, the problem of calculating optimal control in assistant decision-making is converted to a nonlinear problem (NLP). The receding horizontal control (RHC) method is used to ensure that the calculation can be complete in real time. By improving the code feasible sequential quadratic programming (CFSQP) algorithm, optimal results of the NLP problem can be quickly searched. Simulation studies show that the real-time assistant decision-making strategy works well.

Robust Adaptive Backstepping Design for Unmanned Aerial Vehicle Formation Guidance and Control

LI Xue-song1, LI Ying-hui1, LI Xia2, LI Chao-xu1, GUO Chuang1

2012, 30(5):  552-558.  doi:10.3969/j.issn.0255-8297.2012.05.018

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 A robust adaptive backstepping method is proposed for a generic uncertain system, and its application to integrated guidance and control for unmanned aerial vehicle (UAV) formation flight studied. The unmodeled dynamics are compensated by an adaptive neural network. Boundedness of tracking errors is proved by the Lyapunov theory. The leader-follower formation flight guide and control strategy is introduced. An integrated guidance and control law of the UAV formation flight is designed based on the adaptive backstepping and dynamic inversion. A six-degree-of-freedom nonlinear simulation shows that the follower can robustly track the leader with uncertain maneuvering.